<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>position</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .page{
            width: 100%;
            height: 4043px;
            background: url("../img/mooc.png") center top no-repeat;
        }
        .nav{
            width:160px;
            height: auto;
            position: fixed;
            left: 0;
            top:50%;
            margin-top: -100px;
            font-family: 'Microsoft YaHei';
        }
        .nav-li{
            width: 160px;
            height: auto;
            border-bottom: 1px solid #ffffff;
            background: #333333;
            text-align: center;
            line-height: 40px;
            color: #ffffff;
            font-size: 16px;
            cursor: pointer;
        }
        .nav-li ul{
            width: 160px;
            height: auto;
            background: #ffffff;
            display: none;
        }
        .nav-li:hover ul{
            display: block;
        }
        .nav-li ul li{
            width: 160px;
            height: 40px;
            border-bottom: 1px dashed #666666;
            color: #333333;
            text-align: center;
            line-height: 40px;
            position: relative;
        }
        .tit{
            width: 160px;
            height: 40px;
        }
        .list-3{
            width: 160px;
            height: auto;
            position: absolute;
            left: 160px;
            top: 0px;
            display: none;
        }
        .nav-li ul li:hover .list-3{
            display: block;
        }
        .list3-dom{
            width: 160px;
            height: 40px;
            background: #444;
            border-bottom: 1px solid #ffffff;
            text-align: center;
            line-height: 40px;
            color: #ffffff;
        }
    </style>
</head>
<body>
    <div class="page">
        <div class="nav">
            <div class="nav-li">
                <div class="tit">慕课网的导航</div>
                <ul>
                    <li>
                        二级栏目
                        <div class="list-3">
                            <div class="list3-dom">三级栏目</div>
                            <div class="list3-dom">三级栏目</div>
                            <div class="list3-dom">三级栏目</div>
                            <div class="list3-dom">三级栏目</div>
                        </div>
                    </li>
                    <li>
                        二级栏目
                    </li>
                    <li>
                        二级栏目
                    </li>
                </ul>
            </div>
            <div class="nav-li">慕课网的导航</div>
            <div class="nav-li">慕课网的导航</div>
            <div class="nav-li">慕课网的导航</div>
            <div class="nav-li">慕课网的导航</div>
        </div>
    </div>

</body>
</html>